It’s not quite as straightforward as that. For a start, our heart rate can fluctuate day to day, depending on our stress and fatigue levels. For example, if you’ve had an especially busy week at work, your resting heart rate may be higher temporarily. As a result, you’ll hit your peak numbers more easily in training (it doesn’t necessarily mean it’s been a more effective session!).
An HR max of 200, at the age of 40, could indicate that you’re a well-conditioned athlete with the ability to achieve incredibly high peak efforts. Or it may be that you’re a ‘beater’ – a person with a naturally high heart rate, meaning it’s easier for you to get to numbers like 200.
While heart rate is generally a good marker for athletic performance, it’s probably more helpful to know what’s happening internally when you pass certain physiological markers – such as what your heart rate is at lactate threshold, or at aerobic base. This kind of information can be gained from scientific lab-style tests where you’re attached to gas analysis equipment.
My advice would be to monitor your heart rate closely when executing different style/intensity sessions, and, unless you’re performing very high-intensity efforts, spend a limited amount of time around 200bpm.